When a blood vessel wall is damaged, collagen fibers from within the wall are exposed. These exposed fibers become a place for platelets to cling to. Platelets are irregular-shaped bodies that help the clotting process by sticking to the lining of the blood vessels. These odd-shaped fragments of cells are normally found floating around your blood along with your red blood cells, kind of minding their own business. But when the cells that line the blood vessels get injured, they release chemicals that cause the platelets to kick into action and become sticky. What we see is layer upon layer of platelets laying down over the wound, somewhat like dirty 'plates' piling up in a sink.
Platelets are like the first responder to a site of an emergency, but platelets can't plug the hole alone. They need some help. This is where we start to see some of the clotting factors that we talked about earlier. One in particular, called fibrinogen, is an inactive clotting factor that helps bind the platelets to form a clot. These inactive clotting factors act as little cross-links, attaching the adjacent platelets to each other. So, in wound healing, platelets take a lot of the glory for being the first ones to the scene, but without their support team, fibrinogen, they would not be able to properly hold together.